Fertilization in species that utilize external fertilization, including model systems such as sea urchin, frog, and fish, all exhibit rapid protein tyrosine kinase (PTK) activation as a critical step required for the sperm- induced calcium transient, exit from meiosis II, pronuclear congression, and mitosis. Recent studies have demonstrated that mammalian eggs differ from lower species as to the mechanism controlling the sperm- induced calcium transient. However, while studies in oocytes of mice and rats indicate that Src-family kinase activity is not required for calcium signaling, there is strong evidence that these kinases play a role in Mil resumption and pronuclear congression. The main goals of this proposal are to establish which Src-family kinases are required signaling pathways critical to MM resumption and pronuclear congression. The first specific aim will test the hypothesis that individual Src-family PTKs (Fyn, Yes, or Src) are required for resumption of meiosis and pronuclear congression. The experimental approach will use a combination of Src-family knockout mice and dominant-negative constructs to define the role of each kinase in these processes. The Second aim will identify the specific biochemical pathways in which these kinases participate to accomplish each function. Here biochemical analyses will establish which pathways have been interrupted by suppression of each individual kinase Fyn, Yes, and Src. The relationship of each pathway to MM resumption of pronuclear congression will be established. The third specific aim will test the hypothesis that Fyn, Yes, and Src are differentially regulated after fertilization and that their activity increases at specific points during egg activation that allow them to control MM resumption and pronuclear congression. This aim will also identify the regulatory mechanisms by which these kinases are activated in the fertilized egg. The results of this study will provide an understanding of the biochemical mechanisms regulating MM resumption and pronuclear congression and will lead to future studies enabling us to modulate these processes artificially. Lay Summary: Fertilization requires that multiple enzymes become turned on in order for the egg to grow into an embryo. This study will use more sensitive, modern techniques to establish which protein kinases trigger the fertilized egg to eject extra chromosomes and move the male and female nuclei together.